Method of determining the proper depth of penetration of a root canal file



July 11. 1967 H. KAHN 3,330,040

ERMINING THE PROPER DE METHOD OF DET OF PENETRAT N OF A T CANAL FI Fi Feb 1964 United States Patent 3,330,040 METHOD OF DETERMINING THE PROPER DEPTH OF PENETRATION OF A ROOT CANAL FILE Henry Kahn, Highland Park, Ill. (25 E. Washington St., Chicago, HI. 60602) Filed Feb. 20, 1964, Ser. No. 346,287 5 Claims. (Cl. 32-57) This invention relates to files for use in filing a root canal of a tooth that is in the'humanmouth, and more particularly to a file having an improved stop means for accurately determining the depth of penetration of the file into the root canal.

A file for filing the root canal of a tooth generally consists of a thin flexible wire-like file that has a handle at one end thereof. The handle may be an elongated rod-like member or it may be short head, which the dentist holds in his fingers as be manually manipulates the wire file within the root canal. It is important that the wire file'extend to the very end of the root canal in order that there shall be completion of the filing, and that it shall extend no further than the end of the root canal, for if it does extend beyond the root canal it may injure delicate tissues. In order to assure this, it is customary to apply a stop to the wire file, the position of the stop being adjustably fixed with respect to the free end of the file so that only the correct length of file extends from the stop. Stops of this kind have generally acted against the crown of the tooth to limit the depth of penetration of the file into the root canal. The exposed crownof the tooth is generally of an irregular shape and at a considerable distance from the root canal. The file extends through an opening that has been drilled in the crown. The portion of the file between the root canal and the exposed cr-own faoe frequently has a limited amount of' permissive lateral movement. As a result, upon successive reciprocations of the file by the dentist, there is no assurance that the stop on the file will each time stop against the same portion of the crown. If the stop comes against a different portion of the surface of the crown, the file may penetrate into the root canal a different amount. A difference of one millimeter in the extent of penetration of the end of the file on successive reciprocations of the file within the root canal can be highly detrimental.

It is one of the objects of the present invention to provide a stop that is applicable to a flexible Wire file of the above mentioned character wherein the stop may be easily flexed to conform with the flexing of the wire and is so constructed that in manipulation of the file the end of the stop bears against the pulpal floor of the root canal. This is a fixed point and will constitute exactly the same stop position for the file for every reciprocation thereof.

In accordance with the principles of the present invention, the stop may consist of a coil of very fine wire that is to be adapted to be slipped over the fleXible'Wire file and embrace it closely, and bear against the head thereof. Successive turns of this coil are in contact with one another so that thecoil does not constitute a compression spring. The coil, being a fine wire, may be cut with an ordinary cuticle scissors, and is not subject to distortion in the cutting. Thus the coil may be stretched manually to permit severing of a part thereof by the scissors and after the severing operation the coil springs back to its initial condition where successive turns thereof are in abutment. The coil of approximately the required length (but not less than the required length) is positioned on the wire file. The wire file is then inserted into the root canal to the full extent to which it is insertable, and an X-ray is taken to determine exactly the amount of shortage of penetration of the end of the 3,330,040 Patented I July 11 l file into the end of the root canal. Thereafter, the file is removedfrom the tooth, and the coil is removed from the file and a corresponding amount of length of the stop coil is cut away. The thus foreshortened stop is again positioned on the file and the file again inserted into position in the root canal, and'an X-ray is'again taken. This process is repeated until the X-ray shows that the free end of the file extends its full required distance within the root canal when the stop bears against the pulpal floor. The file is then ready for use.

If the required length of a stop coil has been determined by the dentist for use in connection with one file, it can be removed and used on another'file that is to be used for filing the same root canal where a second file is needed either to utilize a different kind of file wire or to replace an already used file wire.

I have herein spoken of ascertaining the correct length of the stop coil by using an over length stop coil and, after each of one or more successive X-ray pictures, foreshortening that stop coil until the desired length is found by cutting away parts of the coil. As an alternative, a series of stops in the form of coils or flexible tubular elements may be'provided in different'lengths, say in one millimeter graduations. After an X-ray has been taken of a file in position in a tooth to the extent determined by a particular length of stop, and where it is found from the X-ray that that stop is too long, the dentist measures or estimates from the X-ray film the magnitude of the excess length and replaces the'stop by another stop correspondingly shorter.

Each stop coil may have at one end thereof a head made of suitable material, for instance metal, or a suitable plastic, such as polyethylene by way of one example, which telescopes over the 'head or handle portion'of'the file and resiliently grips the same and is thereby held in place but readily removable'therefrom. If desired, cooperating means may be provided on the head of the file and the plastic shell of the stop that telescopes over the head whereby the plastic shell locks to the head on the file but can be manually manipulated by the dentist to remove the same readily.

In accordance with the principles of the present invention, the coil wire stop or tube, as the casemay be, is sufficiently flexible so that it does not interfere with the flexing of the fine wire file where such flexing is resorted to to cause the file to follow the contour of the tooth. The coil wire constitutes a shoulder on'the file, which shoulder is of a diameter only a small amount greater than that of the file wire and therefore it can pass through the opening that'has been drilled in the crown of the tooth for access to the root canal. V

In the drawing:

FIG. 1 is an exploded side elevational view, partially in section, of the root canal file and stop shown preparatory to assembly of the two; 7

FIG. 2 is a longitudinal sectional view of the assembled file and stop;

FIGS. 3 and 4 are sectional views showing the manner of using the assembled file and stop;

FIG. 5 is a side elevational view, partially in section, and showing a modified form of stop and file; and

FIG. 6 is a longitudinal fragmentary sectional view of a further modified form of stop and file.

Refering now in more detail to the drawing, l'designates a root canal file that comprises a flexible file wire 3 having a shank portion 5 thereof, commencing with the tip 7, that is serrated in a conventionahmanner. The end of the file wire 3 that is opposite to the-tip 7 is permanently'secured to an enlarged head 9 that constitutes one end of a file handle 11. The head 9 may be tapered toward the file wire 3 and may'include circumferentially spaced radial ribs '13, for purposes presently more fully appearing. Spaced from the head 9, the handle 11 may be provided with a knurl 15 for ease in grasping and manipulation of the file. The handle 11 illustrated is relatively short as compared to the overall length of the file wire 3, but it will be understood than handles that are considerably longer may be used.

Provided for cooperation with the file 1 is a stop 17 that comprises a coil 19 of spring wire with the successive turns of coil 19 being in contact with each other so that the coilcannot be axially com-pressed. One end of the coil 19 is molded in a tubular hub 21 having an axial bore 23. The hub 21 is formed of a suitable pliable plastic, such as polyethylene.

When the file 1 and stop 17 are assembled to form the instrument shown in FIG. 2, the file wire 3 projects axially through the stop coil 19 and outwardly beyond the free. end or stop shoulder 35 thereof. The hub bore 23 is sized for snug fitting reception of the file head 9, and the ribs 13 may bite into the plastic of the hub 21 to insure a firm friction grip between the head 9 and the hub 21. Furthermore, gripping between the hub 21 and head 9 may be enhanced by the friction between the knurl 15 and the part of the hub 21 telescoped thereover. The end 25 of the head 9 may abut the tapered end wall' 27 of the hub 21 to insure that the hub 21 and head 9 will assume the same relative axial positions each time the file and stop are assembled.

In use, a stop 17 having a stop coil 19 approximately equal to but preferably no less than the required length for the filing operation to be performed is placed on the file 1 as shown in FIG. 2. The file with the stop thereon is then inserted into the opening 29 that has been drilled in the crown of the tooth 31, and the serrated portion of the file wire is inserted into the tooth root canal 33 until the stop shoulder 35 of the stop coil 19 abuts the pulpal Other means may be used for removably securing stop I secured onto the end of the coil to facilitate removal and replacement thereof onto the file head.

While I have herein spoken of starting out with a projected length of file wire 3 which extends beyond the the file into the root canal, namely the distance between the tip 7 and the end 39 of the root canal 33.

The file 1 with the stop thereon is removed from the tooth whereupon the stop and file are separated and the stop, having a stop coil 19, is foreshortened in the amount equal to the shortage of penetration, and is placed on the file. When the stop and file are so again assembled, the file head 9 and hub 21 are telescoped together until the head end 25 abuts the hub wall 27 to insure that the file and stop are in the same relative axial posiend of the stop shoulder 35 as less than the length of the root canal, so that the end 35 of the stop coil must be foreshortened to bring the projected end 7 of the file wire into proper position in the root canal, this is not indispensible. For instance, if upon initial insertion of the file wire into the root canal until the stop shoulder 35 engages the pulpal floor, the end 7 of the file wire extends beyond the root canal, that will be revealed by the X-ray and the distance of projection of the end 7 beyond the root canal will also be revealed by theX-ray. 'A. single such penetration of the file wire beyond the root canal is not objectionable. The dentist can measure the extent of penetration of the end of the file wire beyond the end of the root canal and canthen replace the stop wire by a difierent stop' which is longer than the stop wire 19 by an amount equal to the distance that the end 7 has projected beyond the root canal. A single X- ray is generally sufiicient. This X-ray shows the distance between the end 7 of the file wire and the end of the root canal, whether the end of the wire terminates short of the end of the root canal or beyond the root canal, and a measurement of the shortage,,or 'overage, will reveal the extent to which the end 35 of the stop must be moved and its direction of movement with respect to the file wire whereby the file wire will project beyond'the end of the stop shoulder 35 an amount that is precisely equal to the length of the root canal as measured from the pulpal floor.

In the embodiment shown in FIG. 6, the file head 15,

v to' which the file Wire 3 is secured has an externally tions as before. The stop 17 with the aforeshortened stop 7 coil 19 may be provided by either cutting the stop coil 19 of the initially used stop the requisite amount, or alternatively, by using another stop that has a coil which is shorter than the first mentioned stop coil by approximately the requisite amount. In this regard the other stop may be one of a set of stops with coils of different lengths, for example in one millimeter 'gradua tions.

The file with the foreshortened stop is again inserted into the root canal 33 until the stop shoulder 35 abuts the pulpal floor 37, whereupon an X-ray is again taken. The foregoing procedure may be repeated until the X-rays show that the tip 7 is at the end 39 of the root canal when the stop shoulder 35 abuts the pulpal floor 37, as shown in FIG. 4.- The file may now be used. Moreover, once the requisite length of stop coil has been determined, the file may'be removed and replaced with other-files that may be needed, as for example, files of larger diameter or files with difierent types of file wires.

threaded shank 45. The hub 49 of the stop,,to whichvthe stop coil 19 'is secured, has a bore 47 that is internally threaded to thread over the shank 45. This hub is threaded until the end 50 thereof seats firmly against the shoulder 51 of the file head 15, thus limiting the extent of thread of the hub onto the shank and determining the exact position of the end 35 of the stop coil with respect to the end 7 of the file wire. The hub 49 may be plastic which is molded around the end of the coil 19, or it may be metal which is soldered or otherwise secured onto the end of the coil. 19. The hub 49 with its attached stop coil 19 may be one of a series of stops that difier from one another only in the length of the stop wire 19 so that by using difierent stops of, the series difierences are obtained in the distance between the end 35 of the stop and the end 7 of the file wire when the hub 49 is in its fully threaded position on the shank 45. The difierences in effective lengths between successive stops of the series may be any fixed amount, say 1 millimeter. Thus, instead of foreshortening a stop that has been used in making a measurement of the penetrated end of the file wire be yond the pulpal floor, the stop may be replaced by another of the series which is of greater or lesser length to give the proper penetration of the file wire into the root canal when the end of the stop bears against the pulpal These shims thus provided, would each be of an axial thickness of exactly one millimeter.

I have herein discussed changing the effective length of the stop in order to procure the desired effective length of the projection of the file while beyond the stop. This is a convenient arrangement in view of the fact that file wires are now sold in a standard length. The same results can be obtained by standardizing on the length of the stop and providing graduated lengths of file wires.

While the stop element is herein shown as being a coil of wire, it may take the form of a tube of suitable diameter and flexibility.

In compliance with the requirements of the patent statutes I have herein shown and described a preferred embodiment of the invention. It is, however, to be understood that the invention is not limited to the precise construction and method herein shown, the same being merely illustrative of the principles of the invention. What is considered new and sought to be secured by Letters Patent is:

1. In a method of determining the proper length of file wire to be used in filing the root canal of a tooth that has an opening for access to the root canal, the steps including: removably telescoping over the file wire of a file a stop with a part of the file wire extending beyond one end of the stop and terminating in a tip and positioning said stop so that the tip is at a predetermined distance from said one end which may be difierent from that required to cause the tip to be at the innermost end of the root canal when said one end abuts a portion of the tooth, inserting the file wire through the opening and into the root canal and limiting the depth of penetration of the file wire into the root canal by abutment of said one end of the stop with said portion of the tooth, measuring the distance between the tip of the file wire and the innermost end of the root canal, removing the assembled file wire and stop from the tooth and replacing the stop by one of a length that is different than that of the first-mentioned stop by an amount approximately equal to said measured distance and positioning said different length stop so that the tip of the file wire is at another predetermined distance from said one end of the second mentioned stop that is difierent from the firstmentioned predetermined distance by an amount equal to the difference in lengths between the two stops.

2. A method according to claim 1 in which the secondmentioned stop is formed by altering the length of the first-mentioned stop.

3. A method according to claim 1 in which the secondmentioned stop is selected from among a series of stops that are of graduated lengths.

4. In a method of determining the proper length of file wire to be used in filing the root canal of a tooth wherein the crown has an opening therein for access to the root canal, the steps including: telescoping over the file wire an elongated stop in which one end thereof constitutes a stop shoulder, removably securing the stop to the file Wire against relative axial movement so that a part of the file wire projects beyond the stop shoulder and terminates in a free end, inserting into the crown opening said projected part of the file wire and the stop and with said projected part of the file wire projecting into the root canal and the stop shoulder abutting against the pulpal floor of the tooth and limiting the extent of projection of the file into the tooth, measuring the distance between the innermost end of said projected file part and the innermost end of the root canal, removing the assembled file wire and stop from the tooth, and providing a telescopically assembled file wire and stop in which the shoulder on the stop is located in a position axially spaced from the first mentioned stop shoulder position an amount equal to the said measured distance to provide a projected file wire part the length of which is equal to the length of the root to be filed as measured from the pulpal floor.

5. In a method of filing the root canal of a tooth wherein the crown of the tooth has an opening therein for access to the root canal, the steps including providing a root canal file wire stop of an external size sufiiciently small to pass through the crown opening'but sufiiciently large to preclude entry into the root canal and with the stop telescoped over the file wire so that part of the file wire projects beyond one end of the stop and with the file wire and stop being secured together against relative axial movement, inserting into the crown opening the projected part of the file wire and the stop and inserting said projected part of the file wire into the root canal, reciprocating the file and stop while the file is in the root canal, and during reciprocation limiting the depth of penetration of the file wire into the root canal by abutment of the stop with the pulpal floor of the tooth.

References Cited UNITED STATES PATENTS 717,594 1/1903 Miles 32-57 1,108,570 8/1914 Gilmore 32--57 1,569,174 1/ 1926 Crowther 128-221 3,209,815 4/ 1962 Roehr 128-221 FOREIGN PATENTS 507,765 7/ 1920 France.

788,884 10/1935 France. 1,297,011 5/ 1962 France.

490,204 12/ 1928 Germany.

837,146 4/ 1952 Germany.

OTHER REFERENCES Cup and Ball Chemopallidectomy Apparatus, in The Lancet, Aug. 23, 1958, page 401.

RICHARD A. GAUDET, Primary Examiner. I. W. HINEY, Assistant Examiner. 

1. IN A METHOD OF DETERMINING THE PROPER LENGTH OF FILE WIRE TO BE USED IN FILLING THE ROOT CANAL OF A TOOTH THAT HAS AN OPENING FOR ACCESS TO THE ROOT CANAL, THE STEPS INCLUDING: REMOVABLY TELESCOPING OVER THE FILE WIRE OF A FILE A STOP WITH A PART OF THE FILE WIRE EXTENDING BEYOND ONE END OF THE STOP AND TERMINATING IN A TIP AND POSITIONING SAID STOP SO THAT THE TIP IS AT A PREDETERMINED DISTANCE FROM SAID ONE END WHICH MAY BE DIFFERENT FROM THAT REQUIRED TO CAUSE THE TIP TO BE AT THE INNERMOST END OF THE ROOT CANAL WHEN SAID ONE END ABUTS A PORTION OF THE TOOTH, INSERTING THE FILE WIRE THROUGH THE OPENING AND INTO THE ROOT CANAL AND LIMITING THE DEPTH OF PENETRATION OF THE FILE WIRE INTO THE ROOT CANAL BY ABUTMENT OF SAID ONE END OF THE STOP WITH SAID PORTION OF THE TOOTH, MEASURING THE DISTANCE BETWEEN THE TIP OF THE FILE WIRE AND THE INNERMOST END OF THE ROOT CANAL, REMOVING THE ASSEMBLED FILE WIRE AND STOP FROM THE TOOTH AND REPLACING 